The invention concerns a magnetic resonance apparatus comprising a superconducting magnet coil which is disposed in a cryostat, and a refrigerator for cooling the magnet coil, the refrigerator comprising a compressor for compressing a working gas, and with a high-pressure line and a low-pressure line disposed between the compressor and a control valve, wherein the control valve periodically connects the high-pressure line and the low-pressure line to at least one connecting line between the control valve and a cold head of the refrigerator, thereby generating pressure pulses through the connected working gas, wherein the control valve and/or connecting line and cold head components are rigidly mechanically coupled to the cryostat.
An arrangement of this type is disclosed in T. Tomaru et al. in Cryogenics 44, pages 309 to 317 (2004). The compressor is disposed outside of the cryostat and is connected to the control valve via the high-pressure line or the low-pressure line. The high-pressure line and the low-pressure line are designed as flexible hoses in order to reduce transmission of vibrations from the surroundings to the cryostat, in particular, to decouple the cryostat from the compressor. The control valve alternately connects high-pressure or low pressure in the form of working gas pressure pulses via the connecting line from one side to the cold head. This periodic changing-over of the control valve generates sinusoidal pressure impact which can result in undesired vibration of the components that are rigidly coupled to the cryostat (e.g. cold head of the refrigerator), or of the cryostat. The frequency distribution of the oscillations resulting from such an arrangement were analyzed by T. Tomaru et al. in Cryogenics 44, pages 309 to 317 (2004). The vibrations can lead to artefacts in the NMR signals.
It is therefore the underlying purpose of the invention to propose a magnetic resonance apparatus which realizes the supply of a working gas to a cold head using a compressor in such a manner that the artefacts in the NMR signals produced by the above-described vibrations are minimized.